(It's been over four years since I watched Mekaku City Actors and it wasn't the most coherent anime, so please forgive me if I've gotten any details wrong or missed something obvious.)

In the episode "Heat Haze Daze", Hibiya and Hiyori are trapped in an infinite time loop in which Hiyori keeps dying, and Hibiya keeps trying and failing to save her. They finally break out of the time loop (I presume) when

Hibiya sacrifices himself to save Hiyori's life.

The next time we see them is when Haruka breaks open the back of a van to find them bound and gagged inside. I don't recall there ever being an explanation of how they got there.

What happened to Hibiya and Hiyori between them breaking out of the time loop and Haruka finding them in the van? Who put them there, and why?